It is known to use disposable plastic containers to store microwaveable foods. The typical food container of the prior art consists of a clear or solid color base and a clear lid. The clear lid of the prior art plastic food container allows visible inspection of the container contents. The lid and base of the prior art plastic food container may be separate articles or may be hingedly attached to each other.
The lid and base of the prior art plastic container have complementary interlocking rim structures that seal the container. This interlocking rim arrangement is essential in preventing leakage and spillage of food contents from the container. In addition, this interlocking rim arrangement promotes heat build-up inside the container during microwaving or retains the temperature of hot foods placed in the container. When hot foods are placed or cooked in the container, high pressures can develop inside the container. Such high steam pressures can pose a hazard to consumers should the lid be purposefully or inadvertently opened. Additionally, if the pressure builds up sufficiently, it can cause the lid to explosively separate from the base. This explosive separation can, in turn, cause the sudden ejection of hot and messy food contents.
The solution to preventing excessive steam build-up is not simply a case of providing the container lid with vents. In this regard, the lid of some prior art plastic food containers may contain top surface holes or vents. Often the vents are in the form of cruciate slits. The cruciate slits form near-circular tabs that can be deformed upward to permit egress of steam formed inside the container. Though these slits assist in the venting of steam gases from the container, they also permit the leakage or spillage of food contents should the container tip or turn over. They also allow the ingress of bacteria into the container.
To eliminate the problems associated with slit venting, some manufacturers have provided one of the rim structures (usually that of the lid) with transverse channels that allow steam to escape through the channels when the lid rim and base rim are engaged. These channels create a permanent discontinuity in the seal between the lid rim and base rim. Liquid food contents can pass through these channels when the container is tipped. Accordingly, the problem with these types of rim egress channels is that the container is not leak resistant.
Other container manufacturers have designed containers that eliminate excess steam pressure via a two-position, lid rim and base rim engagement mechanism. In the first position, the lid rim and base rim engage, sealing the container. In the second position, the lid rim and base rim assume an orientation under which steam may vent through the rims. In the case of these latter containers, the sealed lid assumes its venting position on the base either through manual repositioning or by the lifting action of rising pressure inside the container. Once the lid is in the venting position, steam can escape the container by flowing through the rim structures and out through the container. The drawback to these prior art venting solutions is that once the lid is positioned in or assumes its secondary venting position on the base, the container is only loosely closed and no longer leak resistant. There is thus a need in the art for a plastic food container that allows for the venting of steam pressure, but restores itself to a leak resistant state once excess steam is purged from the container.